LAS VEGAS — In the year before Las Vegas gunman Stephen Paddock carried out the worst mass shooting in modern US history, the high-stakes gambler appeared to have become increasingly unstable and distant, and complained of being sick, according to a final investigative report released Friday.

Financial records also showed Paddock had lost more than $1.5 million in the two years before the Oct. 1 shooting that left 58 people dead and more than 800 others injured.

One of Paddock’s brothers told investigators that he believed the gunman had a ‘‘mental illness and was paranoid and delusional,’’ and his doctor believed he may have been bipolar.

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Despite the revelations, police say they are closing their investigation without a definitive answer for why Paddock amassed an arsenal of weapons and unleashed gunfire from a hotel suite onto a concert crowd below.

‘‘What we have been able to answer are the questions of who, what, when, where and how,’’ Clark County Sheriff Joe Lombardo said. ‘‘What we have not been able to definitively answer is. . . why Stephen Paddock committed this act.’’

Paddock was the only gunman, and he didn’t leave a manifesto ‘‘or even a note’’ to answer questions about his motive, the sheriff said.

With the final report released, the Las Vegas Metropolitan Police Department has closed its 10-month investigation and no one else will be charged, said Lombardo, the elected head of the agency.

Earlier this year, US prosecutors charged a man accused of selling illegal armor-piercing bullets found in Paddock’s room at the Mandalay Bay hotel-casino on the Las Vegas Strip. Douglas Haig has pleaded not guilty and maintains he sold tracer ammunition, which illuminate a bullet’s path.

In a separate development, a group of survivors of the mass shooting at the Marjory Stoneman Douglas High School in Parkland, Fla., will hold a rally Saturday outside the Virginia headquarters of the National Rifle Association.

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The group is halfway through its national bus tour aimed at registering young people to vote and raising awareness about gun violence.

The teens will be joined Saturday by activists, protesters, and survivors of gun violence to protest the NRA’s role in blocking gun-control laws and defending sales of guns like the AR-15, the semiautomatic rifle used in the Parkland massacre.

The protest, dubbed the ‘‘National March on the NRA,’’ will begin at noon. It is expected to last three hours.

Demonstrators say they have several number of demands and policy proposals.

They are seeking a ban on high-capacity magazines and semiautomatic rifles and long guns that use self-loading magazines. They want universal background checks through the National Instant Criminal Background Check System. They also want a searchable database of gun owners run through the Bureau of Alcohol, Tobacco, Firearms and Explosives.

Protesters say they will demand that the Internal Revenue Service revoke the nonprofit status of the NRA and that the House Appropriations Committee approve funding for the Centers for Disease Control and Prevention to research gun violence and its impact on public health and safety.

In Chicago on Thursday, about 200 demonstrators briefly shutdown Chicago’s Lake Shore Drive as they marched through one of the city’s more affluent neighborhoods to draw attention to gun violence in the city’s poorer areas.

Organizers hoped the march would draw attention to violence, corruption, and the lack of economic investment in the city’s African-American neighborhoods. The protesters also demanded the resignation of police Superintendent Eddie Johnson and Mayor Rahm Emanuel for failure to stem gun violence.

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Johnson has asserted in recent weeks that violent crime in the city has declined, attributing it to new police tactics. However, he conceded more has to be done in the neighborhoods where much of the violence takes place.

‘‘There are too many killings in Chicago; there are too many police-involved killings in Chicago,’’ said Tio Hardiman, one of the demonstration’s organizers. ‘‘It’s time to change the narrative in Chicago.’’

City plows and garbage trucks blocked lanes on Lake Shore Drive in the vicinity of the protest. It brought traffic to a standstill as motorists were forced to exit the roadway.

After protesting on Lake Shore Drive, the demonstrators marched to Wrigley Field as fans were arriving for a Chicago Cubs game, snarling traffic and attracting onlookers.